The present invention relates to power meters and, more particularly, to a power meter to which the collective current draw of multiple loads is measured using a measuring circuit composed entirely of analog components.
Whether it be as a matter of general interest or to determine the size needed for an auxiliary power supply, such as an electric generator, homeowners are increasingly interested in the energy use associated with the electric load of the home and, more particularly, of selected electrical loads. The total electrical load of a home may be determined through monitoring the utility power meter typically located exteriorly of the home. However, determining the electrical load, i.e., current draw, of selected electrical loads is more difficult.
One approach is to electrically isolate all loads except those to be tested and then visually inspect the utility power meter. A drawback of such an approach is that all loads not to be measured, of which there may be dozens for a single home, must be electrically isolated. Alternately, the circuit breakers for the circuit branches loaded by the electrical devices not to be measured may be thrown OFF. In the case of the latter, the homeowner would still be required to electrically isolate loads of a given circuit branch if other electrical devices that load the given circuit are to be measured. Regardless of which approach is taken, it can be time-consuming to electrically isolate the appropriate electrical devices. Moreover, if the homeowner wanted to measure the energy usage over time, the electrical isolation would be required throughout the measurement interval, which may be undesirable and impractical.
As such, a number of in-line power meters have been designed that allow current to be supplied to an electrical device through the power meter itself when interconnected between a wall outlet and the electrical device. These devices typically include rather complex digital circuits that measure various electrical parameters associated with the energy usage of an electrical device, such as an appliance. These parameters include instantaneous values, such as instantaneous current, as well as time-based values, such as average current. Moreover, some power meters may be programmed to include cost information associated with energy usage so that a homeowner can monitor the cost of the energy usage of a given electrical device.
These conventional power meters, which can be quite costly to the consumer because of the complexity of the measuring circuitry and the functionality provided, are designed to be wall-connected devices. That is, the power meter will include a back-mounted electrical plug that plugs into a conventional wall outlet. The power meter will also include a single front mounted outlet into which the electrical plug of an electrical device to be measured can be plugged. Outside their cost, these conventional power meters are generally practical if the outlet to which the power meter is connected is accessible and viewable.
For example, most homeowners connect the power cord of a refrigerator to a wall outlet that is positioned behind the refrigerator. Thus, to make use of a conventional power meter, the homeowner would be required to wheel the refrigerator away from the wall a sufficient distance for the homeowner to connect the power meter. To be able to read the power meter, the homeowner would also be required to wheel the refrigerator out a sufficient distance so that the display panel of the power meter could be viewed. For a typical refrigerator, this may require that the homeowner wheel the refrigerator several feet away from the wall outlet. To measure the energy usage over time and be able to visually read the display panel, the homeowner would be need to keep the refrigerator wheeled away from the wall outlet or wheel the refrigerator away each time the homeowner desired to read the power meter.
Another drawback of conventional power meters is that a single outlet is provided for connecting a single electrical device to the power meter. To measure the electrical usage of multiple electrical devices requires the homeowner to connect each of the electrical devices to a multi-outlet receptacle and then connect multiple electrical devices to the multi-outlet receptacle. The power meter may measure the collective energy usage, but the power meter would have to be positioned in sufficient proximity to all of the electrical devices to be measured. Alternately, multiple extension cords could be used to link the electrical devices to the wall-mounted power meter with the additional cost and disruption associated with multiple extension cords strewn about the home.